1. Field of the Invention
The present invention relates to an imageable composition. More particularly, the present invention relates to a thermally imageable composition having an acid curable composition, an acid generator, an infrared absorber and optionally, a colorant, such as, a colorant dye or a colorant pigment, provided that either the infrared absorber, the colorant or both have a counter anion derived from a non-volatile acid. Sulfonic acids can also be added to increase the speed of the thermally imageable, pre-heated, negatively working patterning compositions, which are useful especially in printing plates.
2. Description of the Prior Art
Printing plates having a coating of a thermally imageable composition that includes an acid curable composition and either a “free acid” cure catalyst or a “latent acid” cure catalyst, such as, an acid generator, are known. However, each of these systems suffers from disadvantages, which include difficulty of controlling the cure rates.
The difficulty of controlling cure rates becomes even more acute if the one or more ingredients of the thermally imageable composition have counter anions that are derived from a volatile acid. Thus, if an ingredient of the thermally imageable composition has a counter anion, such as, a halide ion derived from a volatile acid, the halide ion is converted to the volatile acid by combining with a proton under the strongly acidic cure conditions to produce the non-volatile acid. The volatile acid, for example, HF, HCl, HBr or HI, would then be easily volatilized and lost under the conditions of thermal imaging and subsequent baking, thereby reducing the cure rate. If “latent acid” cure catalyst having a counter anion derived from a volatile acid is used, the cure rate would also be reduced to unacceptably low levels because of the loss of the volatile acid under the conditions of thermal imaging and subsequent baking.
U.S. Pat. No. 5,965,319 and Japanese Patent Application JP 10-039,509 describe a negatively working composition having an IR absorber, novolak and resole resins, and an iodonium, sulfonium or diazonium salt, with a sulfonate group as counter ion. There is no teaching that the presence of sulfonic acid as a discrete additive or the presence of a dye having a counter anion derived from a non-volatile acid, such as, D11 dye, will improve cure rate and processing latitude.
U.S. Pat. No. 6,042,987 describes a thermal negative system in which an acid is produced from a typical generator upon exposure to IR radiation. This promotes cross-linking between a novolak and a crosslinking species.
Japanese Patent Application JP 11-268,438 describes a thermal positive plate having a novolak resin and an IR absorber that has a thermally decomposable sulfonate directly attached thereto. At unimaged regions of the plate, the absorber acts as an insolubiliser and, at imaged areas, it acts as a dissolution accelerant. Japanese Patent Application JP 10-193,554 describes a negative plate having excellent run length by virtue of a new, improved polymer. Japanese Patent Application JP 3-291,665 discloses conventionally imaged negative plate systems. There is no disclosure of dyes, such as, D11 dye, which has counter anions that combine with protons to produce non-volatile acids.
U.S. Pat. Nos. 5,340,699 and 5,919,601 describe imageable compositions having a binder, a crosslinker, an acid generator and an infrared absorber. These patents do not describe the use of a strong acid in addition to the acid generator or that added sulfonic acids would improve plate speed or processing latitude. Further, even though an IR dye having a p-toluene sulfonate anion is disclosed, it is not disclosed that this anion will improve plate speed or processing latitude by combining with a proton to produce a non-volatile acid.
U.S. Pat. No. 5,641,608 describes ablative and positive/negative solubility differential systems for PCB precursors. The negative systems rely on adding an amine active ingredient just prior to use, or by employing a “UV flood then IR exposure” process. U.S. Pat. No. 5,763,134 describes a composition having an acid generator, typically a triazine, and a squarylium dye having a defined nucleus. European Patent Application EP 632,003 describes MeO—and Me—containing phenol compounds for use as improved heat curing additives in conventional positive plates.
None of the above disclosures teach or suggest that the presence of a strong acid, such as, a sulfonic acid, and/or the presence of dyes, such as, D11 dye, which has counter anions that combine with protons to produce non-volatile acids, will improve cure rate and processing latitude when included in the composition.
Accordingly, it is an object of the present invention to improve the speed and processing latitude and robustness of thermal, pre-heated, negatively working patterning compositions, especially printing plates, while maintaining adequate shelf life.
The present invention provides such an imageable composition, which has an improved cure rate, processing latitude, processing robustness, long shelf life of the acid curable composition and moderate energy requirement of the acid generation step.